The present invention relates to a system and method for controlling an/or compensating noxious emissions from an internal combustion engine. More specifically, the invention relates to the control of NOx emissions from a diesel engine.
It is well known that internal combustion engines generate noxious gases as combustion by-products, among them, the oxides of nitrogen such as NO and NO2, or commonly referred to as NOx. It is certainly desirable from an environmental standpoint to limit the quantity of noxious gases generated during an engine combustion cycle. Over the years, various environmental regulatory agencies have imposed emissions standards on internal combustion engines. These standards have become steadily more stringent over the years.
One common approach to meeting these emission standards involves the use of a catalytic converter connected to the engine exhaust. This catalytic converter essentially purifies the exhaust gas emitted from the engine. Of course, there is a limit to the amount of purification that a typical catalytic converter can achieve, complicated in the case of the desired NOx reduction reactions, by the excess O2 inherent in diesel exhaust gas.
In another approach, a fraction of the exhaust gas can be recycled back to the engine""s intake charge (air+EGR) flow using a well-known exhaust gas recirculation (EGR) system. This exhaust gas recirculation approach substantially reduces the NOx component of the exhaust by substituting inert combustion products for some of the excess intake charge (air+EGR) O2, thereby limiting the NOx promoting peak combustion temperature and excess O2 availability for the subsequent combustion process; however, the EGR system can only reduce, but not eliminate all noxious pollutants from the engine exhaust. The inherent tradeoff between NOx formation and particulate formation/oxidation process demands that optimization occur resulting in the needed emission regulation compliance at the best overall performance level for the engine user. The optimization process is complicated by increasing degrees of hardware and software (control) freedom and available to the engine developer coupled with broader and more complex compliance requirements imposed by regulators.
A further approach has been to optimize the air-fuel ratio, which can ultimately optimizes the combustion process. Optimized combustion can significantly reduce the noxious emissions from an internal combustion engine.
While many systems have been developed to address emissions compliance, these systems are frequently obsoleted by new, more stringent emissions regulations. Moreover, the ability for a particular system to consistently reduce noxious emissions is affected by deterioration of the components of that system. Furthermore, the performance of any emissions reduction system is dependent upon the ambient conditionsxe2x80x94i.e. fresh air temperature, pressure and humidity.
In view of these difficulties, there remains a consistent need for an emissions control/compensation system and method that can adapt to these changing needs.
These difficulties are addressed by the present inventive system and method for controlling noxious emissions, such as NOx, from an internal combustion engine. The invention utilizes a closed loop and/or an open loop control algorithm to control one or more compensating levers, each compensating lever corresponding to a controllable engine operating parameter that when changed yields a change in the NOx emissions. The compensating levers can be, for instance, start of injection, variable geometry turbine position, waster gate/exhaust throttle openness, or other engine operating parameters that have an effect on the composition and quantity of pollutants in the engine exhaust.
In the closed loop control approach, the mass flow rate of the NOx is compared to a predetermined target to obtain a delta value. This delta value is applied through a PID controller to generate a corresponding change in one or more of the compensating levers. In certain embodiments, this change value can be supplied directly to pertinent engine control routines within an engine control module (ECM).
In other embodiments, an open loop approach is utilized in which predetermined relationships are generated between one or more controllable engine operating parameters, or compensating levers, and changes in a measure of the noxious emissions. In the open loop approach, a current value for one of the levers is compared against a nominal value, such as a value related to emissions regulatory standards. The change in this value can be evaluated according to a predetermined relationship between the change in the operating parameter and the resulting change in the emission level. This relationship then produces a NOx delta value corresponding to that change in emission level. Thus, with the open loop approach, the current measure of the NOx is essentially inferred from the current values of engine operating parameters. This in contrast to the closed loop approach that relies upon generating an actual measure of the subject emissions and comparing that actual measure with a commanded value.
In one embodiment of the open loop approach, only one such engine operating parameter or compensating lever is sensed and used to generate a NOx delta value. In other embodiments, two or more engine operating parameters can be used to generate two or more emission delta values, based upon corresponding predetermined relationships. In one aspect of the invention, the emission delta values are normalized values so that they are indicative of the effect on emissions without regard to the triggering operating parameter. Thus, in this embodiment, the multiple emission delta values can be combined into a composite delta value. This composite value can then be applied to the inverse of the predetermined relationship for a desired compensating lever to determine a change command for that lever.
It is one object of the invention to provide a system and method for controlling an internal combustion engine to reduce the level of certain pollutants in the engine exhaust. Another object resides in features that control certain engine operating parameters that generate desirable changes in a measure of these pollutants.
One benefit of the system and method of the present invention is that it can combine the benefits of open and closed loop control approaches. Another benefit is that the inventive system can account for degradation of engine components and can be readily modified to account for more stringent emissions regulations.
Other objects and benefits of the invention can be discerned from the following written description and accompanying figures.